As is known, an electronic semiconductor device, for example, an integrated circuit, is formed by a chip of semiconductor material which contains the active portions of the device. The integrated circuit also includes a structure for supporting the chip and for forming electrical interconnections thereby enabling the device to be connected to an external circuit.
Upon completion of its manufacture, the chip has a surface covered by a layer of insulating material. On the surface of the insulating material, metal interconnection elements appear in the form of pads which define the terminals of the electronic device.
An interconnection technique known as the "flip-chip" technique provides for a flat mounting substrate of insulating material on which there are metal tracks which terminate in areas arranged in a configuration mirroring that of the pads on the chip. A soldering material, for example, an alloy of lead and tin, is applied to the pads and, typically, takes the form of a hemispherical projection (a bump) on each pad. The chip is then placed on the mounting substrate with the pads mounted by the bumps in registry with the terminal areas of the metal tracks. The assembly is brought to the melting point of the soldering material so that the soldering material melts and, after cooling, solders the pads of the chip to the corresponding metal areas of the substrate. Finally, a thermosetting resin capsule is formed, incorporating the chip.
In comparison with another widely used interconnection technique which uses thin wires soldered at one end to the pads of the chip and at the other end to the metal terminals which form part of a terminal structure (a lead frame) which surrounds the chip, the "flip-chip" technique has various advantages. In particular, it enables contact pads to be arranged over the entire area of the chip and not only along the perimeter as is necessary with the other technique. The flip chip approach also permits very short interconnections and, finally, it takes up little space.
However, it may not be suitable for use in power applications in which the chip of semiconductor material is subject to a very high degree of heating. This is so since very little heat is dissipated from the chip to the substrate. The chip is joined to the substrate by only a few points with low thermal resistance which are the soldering points. Most of its surface is separated from the substrate by a space which is filled with the resin in which the chip is incorporated. Although the space is very shallow, the heat dissipation is limited by the relatively high thermal resistance of the resin.
To reduce the thermal resistance of the resin, it is known to include therein particles of material having lower thermal resistance. Even this measure does not greatly improve the performance of the device in power applications.